The acidulation, or acidification, of tall oil soap is an important process for manufacturing crude tall oil. Tall oil soap, which contains salts of resin acids and fatty acids, is produced as a chemical by-product of the kraft pulping process of coniferous woods, especially pine. The kraft pulping process is described in detail in The Handbook For Pulp & Paper Technologists, G. A. Smook, (1989).
As set forth in U.S. patent application No. 3,901,869, the acidulation of tall oil soap is preferably conducted with carbon dioxide, under pressure. During the acidulation process, excess carbon dioxide utilized therein acquires small quantities of hydrogen sulfide and mercaptans. The excess carbon dioxide therefore cannot be vented to the atmosphere without costly pretreatment, such as scrubbing with a caustic soda solution.
This excess carbon dioxide has significant economical value as a reactant in the acidulation process. One alternative for reprocessing this carbon dioxide is to recompress the gas to the required high reaction pressures. However, such a recompression operation would be costly in itself, since water and entrained material must be removed from the gas stream. Also, the recompression equipment is expensive.
Therefore, a need exists within the art of processing tall oil soap into crude tall oil to develop processing systems that can beneficially use the excess carbon dioxide utilized during the high pressure acidulation reaction. The solution to this problem should itself be one which is economical and environmentally sound.